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Investigation 2 – Concept Day








Space: Investigation 2

Concept Day


In this Investigation, we will briefly review the planets of our Solar System. We will also discuss asteroids, comets, and meteoroids.

We will then discuss moons in the Solar System and finally, discuss Earth’s Moon and the phases of the Moon as seen from Earth.



  • In this slide, a NASA illustration of the eight planets of the Solar System is presented. You will see that the asteroid belt between Mars and Jupiter is included in this drawing. Reference to the asteroid belt will be made in later slides.
  • While an attempt is made in this and other illustrations of the Solar System to show the relative size of the eight planets, one rarely sees depictions of the Solar System in which the distances between planets are to scale. This is because the distances are simply too great to easily show graphically.
  • A mnemonic is a strategy such as a pattern of letters, ideas, or associations that assists in remembering something. A mnemonic to help remember the order of the planets (starting from closest to the Sun) is: My Very Educated Mother Just Served Us Nachos.



  • In this slide, the inner planets of the Solar System are shown. As noted, the inner planets are all rocky spheres with solid crust. Once again, the asteroid belt is included on this slide to show its close proximity to Earth.



  • In this slide, the Outer Planets of the Solar System are shown. As noted, the outer planets are large, gaseous spheres. Although they may look solid, one could not land a spacecraft on any of the outer planets, as they have no solid surface. Also, the outer planets are much bigger than the inner planets.

Note: The following insert is included to show the size relationship between planets. These are approximately to scale for size, but not for position and distance, of course.




Note: In this slide, asteroids are introduced. You may have some familiarity with asteroids, as they have been the topic of several top box-office hit movies.

  • There is no doubt that asteroids have hit the Earth in the past. The extinction of the dinosaurs some 65 million years ago is thought to have involved an asteroid impact. There is no doubt that asteroids will impact Earth again in the future.
  • While most asteroids in the Solar System orbit around the Sun in the asteroid belt, some asteroids have circular orbits that pass among the outer planets. Others have elliptical orbits that pass within the orbit of Earth and Mercury.



  • This slide gives a very brief introduction to comets and meteoroids.
  • As noted, comets are composed of ice and rock and do not give off their own light. Just like other luminous objects in the Solar System, their light is reflected from the Sun.
  • A meteoroid is the name for the family of smaller than asteroid rock and metal fragments that sometimes enter the Earth’s atmosphere. The nomenclature is worth review:
  • Meteoroid: Metal or rock fragments in the Solar System that are mainly derived by the collision of asteroids in the asteroid belt.
  • Meteor: A meteoroid that enters the Earth’s atmosphere. Oxygen in the atmosphere ignites the meteor and it streaks through the sky. Most meteors burn up entirely and disintegrate before reaching the Earth’s surface.
  • Meteorite: A meteor that reaches the Earth’s surface and strikes the ground.  



  • This slide gives a simple overview of the moons of the Solar System. Notice a moon is a satellite that orbits a planet. Therefore, a comet is not a moon since it orbits the Sun. In this slide, three of Saturn’s moons are seen.

Note: You may be surprised at the large number of moons there are in the Solar System. We are not sure exactly how many moons there are around the outer planets and new ones are likely to be discovered in your lifetime.



This slide shows a rather dramatic event. According to the “Big Splash” hypothesis, about 4.5 billion years ago, a Mars-sized body sometimes called Theia impacted the newly formed Earth.

On impact, a massive amount of debris was expelled into space. Some of this debris gravitated together, forming the Moon, which in turn was captured by Earth’s gravitational field and has been in orbit around our planet ever since. This hypothesis of the Moon’s origin has very recently received supportive evidence as non-Earth-derived materials have been identified in Moon rock samples.

This type of moon formation is probably very common around the galaxy and Universe.



  • This very simple slide shows the relative size and distance scale of Earth and its Moon. When looking at this image it is hard to imagine that the gravitational pull of the Moon on the Earth is still great enough to cause the tides of the oceans!



  • This slide is a composite image of the phases (lunar cycle) of the Moon. It also highlights the nomenclature given for each of the Moon’s phases.
  • In practice, the New Moon may be difficult to see. “Waxing” in the context of Moon phases means “growing in size”. The lightened surface of the Moon is thus waxing between the New and the Full Moon. The “crescent” is when less than half of the surface of the Moon we see is illuminated. “Gibbous” is when illumination is greater than half of the surface that we can see from Earth.
  • Thus, after the New Moon, we see a Waxing Crescent Moon where the crescent is lit on the right side of the Moon as we view it. That is, the crescent opens to the left. The First Quarter Moon is when the right half of the Moon we see is illuminated. The Full Moon is when the entire surface of the Moon appears to be illuminated.

Note: We need always keep in mind that since the Moon is a sphere, we only ever see half of it. Thus, on a “Full” Moon, we really only see half of the Moon. That is why we refer to a “Quarter Moon” even though half of the part of the Moon we can see from Earth is illuminated.

  • As the Moon goes from Full to New, it is said to be “Waning”. A Waning Moon appears to be illuminated on the left, while a Waxing Moon appears to be illuminated on the right. The Third Quarter Moon (sometimes call a Final Quarter Moon) comes between the Waning Gibbous and Waning Crescent phase. Interestingly, while we refer to a First Quarter and Third Quarter Moon, we do not use the term “second quarter” Moon. This, of course, is what is referred to as a “Full” Moon.

Note: You will perform experiments in Investigation 2 Lab that will make the phases of the Moon very clear to you.